Nonclassical class I (Ibeta) genes comprise most of the class I genes of mouse and man. Only recently has it become apparent that at least some of these molecules play important roles in the immune response. We propose to focus our studies on the murine class Ibeta molecule, Qa-1. This antigen is polymorphic, expressed ubiquitously, and known to present a synthetic polymer to gammadelta T cells as well as interact with a peptide deprived from Hsp-65 from M. bovis. Conserved residues in the F pocket of the Qa-1 peptide binding groove differ from those of the class Ia consensus. Therefore, our studies will focus on peptides that are recognized by Qa-1 specific cytotoxic T lymphocytes (CTL) with the aim of increasing our understanding of antigen processing and presentation in the class I pathway. One such peptide is controlled by a gene(s) termed Qdm (Qa-1 determinant modifier). We have identified the Qdm-peptide as being encoded by class Ia D-end alleles, except for Dk, and synthetic peptides derived from these molecules are presented by Qa1b to our Qa1b anti-Qa-1b (Qdm- dependent) CTL clones. We will characterize which peptide is identical to the natural peptide eluted from Qa-1b lymphoblasts, and determine the residues in the peptide that are important for binding to Qa-1b. The Qdm- peptide is also eluted from Qa-1a lymphoblasts. Therefore, we will generate Qdm-dependent Qa-1b anti-Qa-1a CTL clones and determine if they recognize the same peptide as the "a anti-b" clones, as well as whether the peptide binds these two Qa-1 alleles in the same manner. The Qdm-negative (Dk) peptide will also be characterized since Qdm-dependent CTL can be generated in H-2k strains. The CDR3 region of the Vbeta and Valpha T cell receptors from this unique panel of alloreactive and peptide-specific CTL clones will be sequenced. As a result of these experiments we will define the first peptide(s) that binds to Qa-1 and is recognized by specific CTL. In addition, the availability fee these unique peptide-specific alloreactive CTL will allow us to determine how the same peptide is presented by two different alleles of an alloantigen as well as compare how peptide vs. alloantigen influence T cell receptor recognition. The Fee peptide is not expressed on RYA-S (Tap-2 defective) cells or lymphoblasts from Tap-1knockout animals. Surprisingly, the peptide is contained in the signal peptide of D-end antigens, and contrasts with other reports where leader peptides are expressed on mambrane class I molecules in cells lacking transporter function. Therefore, we will use the Qdm- peptide as a probe to examine aspects of antigen processing of leader- derived epitopes. This will provide novel information not only on the processing of these antigens, but also on the traffic of leader peptides within the cell.